1. Field of the Invention
The present invention relates to a solid state signal processing device and a signal processor using the same.
2. Decsription of the Prior Art
Conventionally, an X-Y addressing MOS image sensor, an interline CCD, a frame transfer CCD and the like are known as solid state signal processing elements.
Among these elements, a vertical transfer register and a switching element need not be arranged in the frame transfer CCD, unlike the MOS image sensor and the interline CCD. For this reason, the number of horizontal pels on a TV screen can be increased in the frame transfer CCD.
In general, the frame transfer CCD comprises: an image sensing part for performing photoelectric transducing operations; a memory for temporarily storing charge data from the image sensing part; a horizontal shift register for reading out the stored charge data from the memory in accordance with television synchronization and for transferring the data horizontally; and an output amplifier for converting the readout charge data to a voltage signal. An optical means such as a color separation filter for preparing a color signal is adhered to the CCD image sensing part or is formed on a CCD image sensing chip. In particular, a frame transfer CCD having a stripe color filter on the image sensing part is exemplified, wherein the stripe color filter has R (red), G (green) and B(blue) filter elements.
When the number of horizontal pels is about 580, a horizontal transfer frequency corresponds to 10.7 MHz. When a CCD has the number of horizontal elements described above, a luminance signal is obtained by filtering an output signal of the CCD through a low-pass filter (about 3 MHz). The R-G-B signal having a repeating frequency of 3.58 MHz is supplied to sample/hold circuits to perform color separation.
In this case, color signals require an NTSC bandwidth of 500 KHz. In this case, the sampling frequency is 3.58 MHz, so that the signal bandwidth allows reproduction up to the Nyquist frequency. When an object is non-colored or non-chromatic, the luminance signal is not degraded. However, when an object has a high color saturation, the sampling frequency becomes 3.58 MHz (Nyquist frequency of 1.8 MHz), so that a significant foldover distortion occurs, thereby degrading the image quality. In order to solve this problem, the CCD must be driven in response to a clock of 14 MHz under the condition that the number of horizontal pels is 770. The sampling frequency becomes about 4.77 MHz (Nyquist frequency of 2.4 MHz), so that no problem occurs in the normal receiver. However, when the CCD is driven at the frequency of 14 MHz, a problem occurs in the horizontal register, the output amplifier, a clock IC, the color separation sample/hold circuit, and so on.
In order to separate the CCD output signal by the sample/hold circuit into color R, G and B signals, the signal which is subjected to sampling/holding must have a long and valid signal component to some extent. However, when a drive pulse having a duty ratio of 50% is used, the signal component with respect to the clock pulse of 14 MHz becomes theoretically 35 ns. However, when the rise and fall times of the switching element of the drive circuit are subtracted from the signal duration of 35 ns, the valid signal component has at best a duration of 25 ns. Furthermore, when the leading and trailing edges of the clock are excessively steep, a dark current is increased due to heat in the shift register. The valid signal component then has a shorter valid duration. In addition to these disadvantages, the frequency characteristics of the output amplifier must also be considered.
Variations in electrical characteristics of circuit elements in a clock signal generator, and changes in temperature adversely affect sampling. It is thus very difficult to sample the CCD signal.
Assume a one-phase driven horizontal shift register. A potential well and a barrier are included in each one of a virtual electrode and a clock electrode. When the number of pels is 770, 3080 (770.times. 4) divided electrodes are required. In order to achieve this on the image sensing part of 3 inch size, since the horizontal width is about 8.8 mm, the minimum electrode width becomes less than 2.8 .mu.m. This cannot be achieved in accordance with current known micropatterning techniques having a 3 .mu.m standard.
In the conventional color separation sample/hold circuit, three sample/hold circuits for separating the CCD output into the color R, G and B signals and another sample/hold circuit for supplying a proper sampled/held signal to these sample/hold circuits are required, resulting in complex construction.